The present invention relates generally to the video signal processing art. More particularly, the present invention relates to the improved processing of digital color video information for display on a color television monitor.
Color video monitors are presently used in a number of environments. Although sometimes used in the home entertainment environment, color video monitors are more frequently used in conjunction with a controlled local input signal such as would be generated by a computer. In such a situation, varied demands may be made for flexible adaptation of a basic video monitor to a number of different computer systems. Accordingly, it is desired to have a color video monitor which may be readily and inexpensively adapted to be compatible with a large number of computer systems.
The present standard for color video display is frequently referred to as "sixteen color". As the name implies, sixteen color video information may be processed to allow for display of sixteen different colors on the video display tube. The generation of the actual colors on the picture screen may be accomplished by a video processor in any number of methods as are well known in the art.
As is well known in the digital processing art, a four bit digital signal is required to define a sufficient number of states to identify sixteen separate colors for activating the appropriate video color generation for display. However, the typical video processing system relies upon just three inputs, red, green, and blue (RGB). This limits the typical digital color video system to the eight color states which may be identified by the three bit inputs of a typical digital RGB system. A sixteen color digital system may be achieved by adding a fourth bit, which may typically be referred to as an intensity bit (I) to obtain an RGBI video system.
In one such sixteen color, four bit system, the intensity bit may be used to add an additional component of "white" color to any of the red, green or blue components of the typical system. Accordingly, when the intensity bit is high, a white component will be added to the red, green or blue which will cause any of those colors to be a shade brighter than would typically be generated. For example, a normally pure red signal would become pink and a normally pure blue signal would become light blue. In contrast, when the intensity bit was low, no additional light component would be added to the original signal and pure red would appear as normal red and pure blue would appear as normal blue. In such a system, the eight colors associated with the three bit, eight color system may be generated and a correspondingly brighter shade of each of those eight colors may likewise be generated.
Once the sixteen different colors are identified, it is desirable to be able to control the resultant picture's "vividness" or image strength. Accordingly, it is desirable to have circuitry compatible with digital input signals that can vary the overall image strength. It may also be desirable to provide circuitry for separately controlling the impact or weight of the various components of the video information, such as the intensity information, to further control the displayed image.
Additionally, it may be desired to generate or provide somewhat altered colors than would typically be associated with the eight or sixteen color system. For example, a new "brown" color may be desired at the end video picture. Accordingly, it is desired that an RGB processing circuit be able to distinguish those input conditions under which a different color is desired and appropriately identify the same for the video processor.
Furthermore, it is desirable that the eight color or the sixteen color video control system be compatible with current video processing systems which are adapted to receive the traditional RGB analog inputs. Accordingly, it is desired to provide a digital RGB control system which may accurately identify any of sixteen different color shades for video processing without requiring additional analog inputs at the video processing stage.
Accordingly, it is the principal object of the present invention to provide desired circuitry and generally overcome the deficiencies in the prior art.
It is a primary object of the present invention to provide a R,G,B,I digital video control system for receiving four bits of digital color video information and providing three analog output signals which, when combined, cause the appropriate, desired color to be displayed by the video processor.
It is still a further object of the present invention to provide for an overall RGB gain or level control in conjunction with the other stated objectives.
It is still a further object of the present invention to provide a second gain control which selectively controls the gain of the intensity in a sixteen color, four bit video system.
It is still a further object of the present invention to provide a digital RGBI intensity control system which is compatible with current video processing systems.